The present invention relates to a hydraulic fluid feeding device for feeding hydraulic fluid to operate a power steering device.
A device has been proposed which utilizes two pumps and a flow change-over valve for, on the one hand, combining the flows from the two pumps to supply them to a power steering device when the delivery rate of each pump is small, and, on the other hand, for switching the flow change-over valve to feed the hydraulic fluid from one pump to the power steering device and to bypass the hydraulic fluid from the other pump to a tank when the delivery rate of each pump becomes large. With such a device, the horsepower requirement to drive one pump may be made extremely small when bypassing the hydraulic fluid from this pump to the tank, and a lower consumption of power may be attained.
However, the power steering device requires a relatively high feeding rate of hydraulic fluid when a high load is exerted thereon, that is, when a high output is required. The device proposed above does not necessarily satisfy this requirement of the power steering device. For example, the pumps are normally driven by the engine, and their delivery rates are increased in proportion to an increase in the rotational frequency. Therefore, when a vehicle is travelling along a winding and steep slope, the flow change-over valve is so switched that the hydraulic fluid from only one pump is fed to the power steering device. Under such conditions, the feeding rate of hydraulic fluid fed to the power steering device may become too small upon abrupt turning of the steering wheel, in the clockwise or counterclockwise direction, adversely affecting the steering response.